About the Keck Long Wavelength Spectrometer (LWS)

LWS is a Keck facility instrument offering diffraction-limited imaging
and spectroscopy in the 3-25 µm range from the forward Cassegrain
focus on Keck I. The instrument is currently being recommissioned following
the installation of a new detector, a Boeing 128² Si:As moderate-flux
BIB array.

The LWS dewar is an ``uplooker,'' meaning that the instrument looks
directly at the telescope secondary with no tertiary mirror. All optical
components behind the dewar window are cooled to liquid helium temperature,
except for the detector which is maintained at 8.52±0.02 K via a
precision closed-loop thermal control system. All 10 reflecting surfaces
inside LWS are gold coated for high reflectivity (1% loss per surface).

A rotating grating turret contains the low- and high-resolution gratings,
plus a mirror for direct imaging. The plate scale of 0.08 arcsec/px adequately
samples the 0.25 arcsec (FWHM) diffraction limited
point spread function at 10 µm while providing a 10.2×10.2
arcsec imaging field of view. Two gratings enable spectroscopy at resolutions
of R=100 (blazed at 10.0 µm) or 1400 (blazed at 19.5 µm) over
the 3-25 µm range. Chopping and chop/nod observing modes are both
available.

The LWS control system features a complete graphical user interface
(GUI) at the top level which interacts with the instrument via a keyword
interface. The keyword system follows the standard Keck architecture that
allows the user to inquire and manipulate the instrument and telescope
from the command line. The GUI includes an IDL-based ``quicklook'' image
display and analysis tool, plus other windows which control the instrument
and telescope configuration (e.g., chop-nod frequency and throw).

Principal Investigator:
(UCSD)

CARA Contacts:
(primary),
(secondary)

Current Status: Commissioned and available for observing as of semester
1999B